Ukraine's military chief has told his US counterpart that the country needs to strengthen its air defense system capabilities.

Commander-in-Chief Valerii Zaluzhnyi said on social media on Sunday that he had a phone conversation with US Joint Chiefs of Staff Chairman General Mark Milley.

Zaluzhnyi also asked for supplies of ammunition and equipment.

The appeal came after Russian forces carried out large-scale missile attacks with various weapons on Thursday. They included Kinzhal hypersonic missiles, which Russia boasts as one of its most advanced weapons.

The Russian military said its troops had seized control of the eastern side of Bakhmut, a strategic city in the eastern region of Donetsk.

A Ukrainian military commander expressed his determination to fend off Russian attacks, saying his troops have built defense lines on the city's western side.

The commander pointed to the need to gain time to launch a quick counteroffensive.

The British defense ministry noted that Russia continues to suffer extremely heavy casualties in Ukraine, and the impact varies considerably across Russia's regions.

The ministry said in its intelligence update on Sunday that "the richest cities of Moscow and St Petersburg have been left relatively unscathed."

The ministry also said, "In many of the Eastern regions, deaths are likely running, as a percentage of population, at a rate of 30-40 times higher than in Moscow."

It added that as the Russian defense ministry "seeks to address its continued deficit of combat personnel, insulating the better-off and more influential elements of Russian society will highly likely remain a major consideration."